1. Field of the Invention
The present invention relates to an article comprising a vacuum insulation panel within extruded thermoplastic polymeric foam and a process for preparing such an article.
2. Description of Related Art
Thermal insulating panels offer thermal barrier properties desirable for enclosures having regulated temperatures, including houses, offices, refrigerated containers and the like. Extruded polymer foam articles such as polystyrene foam boards are common thermal insulation materials for use in such enclosures including building and construction applications as well as thermal insulation containers. Extruded polymer foam articles are easy to handle and shape at a job site and are a familiar material to those in the construction field. Even so, it is desirable to have a polymer foam-like article that has a lower thermal conductivity than present polymer foam.
Halogenated blowing agents are desirable for preparing extruded thermoplastic polymer foams for thermal insulation at least partially because halogenated molecules provide foam having a low thermal conductivity. However, there are increasing regulations on the use of halogenated molecules for applications such as blowing agents due to perceived harm such molecules have on the environment. Of particular concern is ozone depletion potential (ODP) and greenhouse warming potential (GWP) of halogenated molecules. Identifying blowing agents that have thermal conductivities as low as halogenated molecules is a tremendous challenge. As a result, it is increasingly more difficult to manufacture thermally insulating extruded thermoplastic polymer foams having desirably low thermal conductivities.
Vacuum insulation panel (VIP) articles are one type of thermal insulating material that has an extremely low thermal conductivity. VIPs comprise a vapor impermeable material (barrier material) that encloses an evacuated space containing an internal matrix material. The vapor impermeable material is typically a metal sheet or a film. The polymer film usually includes a metal coating on the inside and/or outside surface to reduce gas permeability through the film. The internal matrix material is a low density porous material such as open-celled foam or porous particulate material. The internal matrix material maintains spacing within the vapor impermeable material enclosure. That spacing is under vacuum, the vacuum serving as an optimal thermally insulating barrier through the VIP.
VIPs offer attractive thermal insulating properties, but suffer from weaknesses as well. The vapor impermeable material that encompasses the VIP can serve as a thermal short from one side of the VIP to the other. Thermally conducting materials such as metals, which can server as strong vapor impermeable enclosures, also serve as efficient thermals shorts across the VIP barrier. Polymer films containing a thin metal coating are more common as vapor impermeable enclosures for VIPs and offer a less efficient thermal short across the VIP. Polymer films, however, are relatively fragile and upon puncturing or breaching would relieve the vacuum in the VIP and destroy the major thermal barrier properties of the VIP. Despite these weaknesses of VIPs there are methods for using VIPs in building and construction applications.
WO97/11842 offers an enhanced insulation panel comprising a VIP and a frame around the periphery of the VIP to protect the VIP during handling. The frame can be polymeric material, even a polymer foam material.
EP1213406 discloses a thermally insulating wall that contains VIPs between layers of other elements.
EP1500752A2 discloses a thermally insulating element containing a VIP and a protecting layer as well as a fastening element to affix the elements to a building surface.
DE202007014565 discloses a thermally insulating system containing VIPs between layers of other elements.
It would advance the art of thermal insulating panels to provide a panel that has the appearance and feel of extruded polymeric foam and that handles like extruded polymeric foam but that further enjoys thermally insulating properties more like VIPs. Moreover, it would be desirable to have such a panel that contains VIPs but that concomitantly provides localized protection of the VIPs and optimal thermal insulation properties around the VIPs to preclude thermal shorting by the VIP vapor impermeable barrier enclosures.